1. Field of the Invention
This invention relates to a system for rapidly heating selected portions of an integrated circuit package assembly and, more specifically, to such heating using a heat source capable of selectively heating a predetermined portion of an area while the entire area is being subjected to heat-generating radiations from the heat source, the heat source preferably being a tungsten halogen light source.
2. Brief Description of the Prior Art
In the fabrication of semiconductor devices and particularly integrated circuits, it is desirable that the semiconductor chip be heated to temperatures in the range of about 200 to 300.degree. C. prior to wire bonding in order to improve the bonding process. It is also desirable that the lead frame to which a bond is to be made be retained at a much lower temperature than the chip, this lower temperature being sufficiently low to minimize oxidation of the lead frame material, generally copper. Lead frame oxidation generally diminishes the wet solderability thereof, leading to the obvious problems resulting therefrom. This problem has existed in the prior art because the mechanism used for heating of the semiconductor chip, generally a heater block or hot plate, also supports the lead frame and is non-heat selective. Accordingly, both the chip and the lead frame are heated together as a single unit to about the same high temperature, this being the temperature required for bonding to the chip. It is therefore apparent that a system whereby the semiconductor chip can be selectively heated relative to the lead frame while the chip and lead frame are in contact with each other is highly desirable.
A proposed lid sealing apparatus and method by Bokil would replace a metal heater filament with a beam of focused infrared light to reduce heat transfer into the ceramic package. See U.S. Pat. No. 4,481,708 issued Nov. 13, 1984 and U.S. Pat. No. 4,685,200 issued Aug. 11, 1987 OF D. R. Bokil and D. R. Bokil et al., and, the article by D. E. Erickson "Hybrid Circuit Sealing-Problem Prevention Clinic", Electronic Packaging and Production, 22(11): pp. 133-137, November 1982. The Bokil system is relatively large and complicated due to the spacing design required to focus the infrared beams towards the glass for the lid seal and the required number of infrared beams (one on each side of the package).